Emersed or submersed perennial with smooth stems, trailing on ground and forming dense mats.  Grows in water or very wet soils.

Submersed perennial with rhizones, stem branched and somewhat flattened.  Leaves reddish-green, alternate, oblong, with finely toothed edges.  In habits ponds, lakes, and streams.

Several species found in US, often found growing together.  Small floating herb, which grows rapidly to cover surface of still waters.

Submersed prennial, rooting in mud.  Stems branched, usually purple, to 3 meters long.  Leaves in whorls of 3-4, pinnately divided into 6-16 pairs of leaflets.  Flowers unisexual, borne in whorls.  Infests lakes, ponds, streams, and estuaries, fresh and brackish water, up to 5 m in depth.

Free-floating fern, with pair of floating leaves up to 4 cm long.  Leaf surfaces have rows of papilla branching into hairs.  Inhabits quiet waters such as lakes, ponds, oxbows, swamps, and marshes.

Submersed perennial with branched stems to 1 m long, and forming turions and tubers.  Leaves whorled to 15 mm long by 4 mm broad, toothed, red-viened, spinulose on the lower suface.  Infests most water habitats, forming dense mats.

Erect, tall perennial from stout, creeping rhizones.  Stems to 4 m tall.  Leaves flat, smooth on the surface to 5 cm broad.  Large inflorescence (15-40 cm), yellow to purple, blooming from July to September.  Abundant in marshy habitats, often forming extensive colonies.

Erect herbaceous perennial with showy purple flowers.  Prolific seed production aids in spread of the plant.  In winter, dies back to the root crown, and regrows in spring.  Colonizes moist soil to emergent shallow water areas, may even grow in moist upland areas

Fast-growing, floating aquatic plant that can grow up to 16 feet long, forming dense mats. Submerged leaves are feather-like, and emergent leaves are triangular and toothed.  Seeds are covered with sharp, tough spines, and can cause foot injury.

Free- floating plant that is capable of forming dense mats on water surfaces.  Thick leaves closely resembling a head of lettuce.

Floating perennial, rooting at the nodes.  Leaves elliptical to round, up to 20 cm long by 15 cm broad.  Blue-purple flowers borne in racemes, 4-6 cm long.  Infests streams, ponds, ditches, backwater areas.